Patients are stratified according to histology (high-grade glioma vs low-grade glioma vs brainstem or visual pathway glioma vs medulloblastoma/primitive neuroectodermal tumor vs ependymoma). (Brainstem glioma stratum closed to accrual as of 12/21/2000.) (High-grade glioma stratum closed to accrual as of 01/08/2002.)